The impact of environmentally friendly supramolecular coordination polymers as carbon steel corrosion inhibitors in HCl solution: synthesis and characterization

Two 3D-supramolecular coordination polymers (SCP1 & SCP2) have been synthesized and characterized by physicochemical and spectroscopic methods. In a solution of 1.0 M HCl, SCPs were used to prevent corrosion of carbon steel (CS). The inhibition productivity (%η) rises as the synthetic inhibitor dose rises, and the opposite is true as the temperature rises. The study was carried out using chemical (mass loss, ML) and electrochemical ( potentiodynamic polarization, PDP and electrochemical impedance microscopy, EIS) techniques, which showed %η reached to 93.1% and 92.5% for SCP1 & SCP2, respectively at 21 × 10−6 M, 25 °C. For the polarization results, SCPs behave as mixed-type inhibitors. With increasing doses of SCPs, the charge transfer resistance grew and the double layer's capacitance lowered. The creation of a monolayer on the surface of CS was demonstrated by the finding that the adsorption of SCPs on its surface followed the Henry adsorption isotherm. The parameters of thermodynamics were computed and explained. The physical adsorption of SCPs on the surface of CS is shown by the lowering values of free energy (∆Goads < − 20 kJ mol−1) and increasing the activation energy (E*a) values in presence of SCP1 & SCP2 than in their absence. Atomic force microscope (AFM) and scanning electron microscopy (SEM) demonstrated the development of a protective thin film of SCPs precipitated on the surface of CS. There is a strong matching between results obtained from experimental and theoretical studies. Results from each approach that was used were consistent.


Inhibitors and chemicals
Synthesis of ∞ 3 [Cu 2  (CN)  4 (Ph 3 Sn) 2 .dmqox], SCP1 40,41 A solution of 90 mg (0.31 mmol) "K 3 [Cu(CN)4] in 5 ml H 2 O was added dropwise with gentle stirring to a solution of 366 mg (0.95 mmol) Ph 3 SnCl and 50 mg (0.31 mmol) given and dmqox in 10 mL of warm acetonitrile.A yellow precipitate formed immediately.After filtration, washing with small amounts of H 2 O and acetonitrile, and drying overnight, about 314 mg (93.4% expressed as K 3 [Cu (CN) 4 ]) of a yellow precipitate was obtained.All previous attempts to grow individual SCP1 crystals suitable for X-ray examinations have so far resulted in the formation of a microcrystalline powder.Elemental Analysis: Calculated" Calc.for C 50   3 [Cu (CN) 2 Me 3 Sn•qaz], quinazoline (qaz), SCP2 40,41 An aqueous solution of 90 mg (0.31 mmol) "K 3 [Cu(CN) 4 ] was added with gentle stirring to a solution mixture containing 189 mg (0.95 mmol) Me 3 SnCl and 40 mg (0.31 mmol) quinazoline ( qaz) contained in 10 mL Acetonitrile.After two weeks, the yellow prismatic crystals began to separate from the initially clear solution.After filtration, washing with a small amount of cold water and acetonitrile, and drying overnight, 84 mg of SCP2 was where the weights of the samples before and after dipping are m 0 and m, respectively, s is the area (cm2) and t is the time of immersion (min).The following formula can be used to determine S, the surface area of the coins with the corresponding inhibitory efficiency from the ML approach (η w ):

Synthesis of ∞
where ϴ surface coverage is, and ν o and are the corrosion rates of coin specimens in HCl electrolyte solutions without and with a specific additive concentration of SCP1 & SCP2 (g m −2 min −1 ).

Electrochemical measurements
The working electrode that was previously examined is used in the approach, which is a cell with three electrodes 12 ."This electrode has a 1 cm 2 exposed surface area and is composed of CS metal, the process of manufacture for which was previously disclosed 12 .The electrode is prepared in line with the test prior to use, followed by ML and the use of a saturated calomel electrode (SCE) as the reference.Next, the Pt foil auxiliary electrode is used.After 30 min of immersion in the OCP solution, the CS electrode reaches the stability criterion.PDP curve measurements were done in the 250 mV potential range using an OCP scanning rate of 0.2 mVs −1 .The current density is utilized for the measurements in this test.Electrochemical impedance spectroscopy (EIS) measurements were carried out in the frequency range of 10 5 Hz to 0.01 Hz using an AC excitation pulse with amplitude of 10 mV.Electrochemical frequency modulation (EFM) was investigated by sending a signal with a 10 mV capacity across two sinus waves with a frequency range of 2 to 5 Hz 43 .This equipment is quick and nondestructive.Corrosion current density (i corr ), causal factors CF-2 and CF-3, and Tafel slopes (ß a and ß c ) were found through the higher peaks 44 .
The Gamry Potentiostat/Galvanostat/ZRA (PCI4-G750) was the instrument used in the electrochemical research.Gamry includes a computer for data collection together with the DC105 DC corrosion software, EIS300 EIS software, EFM140 for EFM software.Echem Analyst version 5.5 was used to plot, compute, and synthesize the data".At 25 0 C, all electrochemical experiments were conducted.When doing electrochemical measurements, the following formulas are used to determine the inhibitory efficiency: Here i corr(0) and i corr(inh) are the corrosion current densities of coins in aggressive media, respectively before and after the addition of the inhibitor.R ct(inh) and R ct(0) are the charge transfer resistances in the presence and absence of the inhibitor, respectively.

Surface examinations
"The CS samples used for surface morphological tests were prepared in 1 M HCl acid (blank) and 21 × 10 −6 M inhibitors at room temperature for one day after physical abrasion with various sanding sheets up to 1,200 grit, then after 10 minutes After immersion, samples were gently washed with distilled water, dried thoroughly, and placed into prepared samples that were evaluated using a scanning electron microscope (SEM) and an atomic force microscope (AFM)".

Quantum chemical calculations
The calculations from quantum chemical theories were used as a helpful tool for comprehending the material characteristics and the corrosion inhibition procedure, based on a variety of methodologies 45,46 .Density Functions Theory (DFT) was applied using the Dmol3 module in Material Studio software (version 7.0) to explore the whole geometrical optimization of the inhibitors under investigation.Both the efficiency and the corrosion www.nature.com/scientificreports/inhibition behavior of the two derivatives are expressed by their molecular and electronic structures.Quantum characteristics such as electronegativity (χ), dipole moment, chemical potential (μ), smoothing (σ), absolute hardness (η), and the energies of the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals were estimated using the DFT approach.

Monte-Carlo simulations
The best configuration of the investigated compounds on the surface of Fe (1 1 0) was assessed using Monte Carlo simulations.The Fe (1 1 0) crystal surface is thought to be the most stable surface utilized in this simulation, according the literature 47 .In order to examine the adsorption of uncharged and protonated inhibitor molecules, 100 water molecules were used to mimic the solvent action during the corrosion process.First, geometrical optimization of the water and inhibitor molecules was carried out using the quote module.The substrate-adsorbate system's configuration space was searched using a Monte-Carlo method to find low-energy adsorption locations where the temperature is progressively lowered.The total energy, adsorption energy, and substrate-adsorbate energy were calculated using the Monte Carlo simulation.

Results and discussion (ML) measurements
For a specified dipping period, the ML of the samples was measured.This method involves dipping the sample in an acid solution for a certain period of time, after which the sample's level of corrosion is determined 48 .The SCP1 and SCP2 were put through various temperatures and dosages in 1.0 molar hydrochloric acid during the experiments.The results of an investigation that lasted 120 min are shown in Table 1.The results showed that the corrosion rate (C.R.) reduced with increasing inhibitor doses while the rate of inhibition increased with doses from 1 × 10 −6 to 21 × 10 −6 M (Fig. 1).Inspection of Table 1 shows that by increasing the temperature the C.R. will significantly accelerate and thus %η will fall.The % improvement with higher synthetic inhibitor dose can be used to qualify the adsorption of the inhibitor layer on the CS surface.The oxygen and nitrogen atoms of the inhibitor molecules as well as the electrons in the aromatic rings that create free electron pairs make up this layer.This shows that the inhibitor molecules of SCP1 and SCP2 are adsorbed on the metal surface and may mainly belong to physical adsorption, that is, low temperature is beneficial for the adsorption of inhibitors inhibition on the CS surface.The competing adsorption of acid ions on the metal surface becomes more intense at higher temperatures, which improves metal corrosion and lowers inhibitive effectiveness.The percentage inhibition % η) was in this order: SCP1 is superior to SCP2.Equation ( 2) was used to calculate the percentage inhibition of the CS and the degree of surface coverage (ϴ).Table 1 summarizes the information that C.R. and % η collected from synthetic compounds (SCP1&SCP2) at various temperatures and dosages.

Adsorption isotherm behavior
The enhanced % η with a higher doses of synthetic inhibitors can be used to be qualified the adsorption of an inhibitor layer on the CS surface.This layer is composed of pairs of free electrons that are formed by the oxygen and nitrogen atoms in the inhibitor molecules and the π-electrons of the aromatic rings.Physical, chemical, and www.nature.com/scientificreports/reterodonation (where the inhibitor molecules' unoccupied molecular orbitals and the surface metal atoms' dorbitals are involved) adsorption are the three main types of adsorption that can be occurred 49 .The adsorption process becomes more intense if the inhibitor molecules contain heteroatoms like nitrogen, sulphur, or oxygen because these atoms emit one pair of electrons that lead to electrostatic adsorption on the surface of the CS and the formation of an insoluble layer that slows down the dissolution of CS.Using a suitable isothermal technique, the adsorption conditions of the synthesized compounds on the CS surface may be established.To ascertain whether adsorption isotherms were most suitable, data for ML tests were created in several mathematical adsorption isotherm expressions using data recorded at various temperatures.According to this study's findings, Henry isotherm is the most suitable adsorption isotherm for the adsorption of SCPs on CS surface (Fig. 2).This isotherm demonstrates how the θ and inhibitor dosage are related".
This equation C and K ads use symbols to describe, respectively, the dosage of the synthesized chemicals and the adsorption process' equilibrium constant."The Henry isotherm's R 2 value was precisely closer to the unit, according to the investigating data in Table 2.The Henry adsorption isotherm thus provided a good description of the inhibitor adsorption behavior seen on the surface of CS.In Table 2, the term "K ads " stands for "adsorption strength" and "displays the molecular strength of the adsorbed layer."Low values of K ads reflect weaker interactions between the inhibitor molecules that are adsorbing to the CS surface, however this only indicates that the solvent molecules can easily remove the inhibitor molecules from the metal surface".In the current work, the adsorption of molecules in synthetic compounds (SCP1&SCP2) was investigated using free energy and the following formula: The amount of water in the bulk solution is represented by the number 55.5 in this equation when expressed in mol/L 50 ."Table 2 shows the adsorption properties of SCPs.The data in the Table showed the spontaneous adsorption and stability of the double layer adsorbed on the metal surface, which are verified by the negative values of the free energy obtained.The results from ∆G 0 ads show that the sort of adsorption that leads to physical adsorption is known to occur when ∆G 0 ads values are less than 20 kJ / mol, which is consistent with the data found 51 .This is supported by the literature review.Using the Vant't Hoff equation, the following equation for ∆H°a ds and ∆S°a ds can be measured": The correlation between log K ads and 1/T is shown in Fig. 3.The standard adsorption enthalpy change was calculated from the following balance (− ∆H o ads ), and the entropy value was given (− ∆S o ads ): We are aware that the enthalpy values in the current investigation are negative and therefore the SCPs inhibitor adsorption molecules are exothermic.The exothermic process can refer to either physical or chemical adsorption, even though the H o ads values are less than 100 kJ/mol, indicating that the adsorption is mostly physical" 52 .

Effect of temperature
The effect of temperature on the dissolution of CS samples employed in the synthetic compounds and dipped in 1.0 M of hydrochloric acid was studied in the current experiment both with and without various doses of synthetic compounds (1 × 10 −6 -21 × 10 −6 M) at 25-45 °C."It has been demonstrated that the C.R. rises as the temperature rises.From the slope of the graphs, the activation energy (E * a ) was calculated using the Arrhenius Eq. ( 9) 53 .
In contrast, the Arrhenius exponential factor was represented by the letter (A).Arrhenius plots [log (C.R.) against 1/T] are displayed in Fig. 4. The Arrhenius equation, which has a slope of [-E * a /2.303R], is demonstrated by the plot, which yields straight lines with almost unit regression coefficients.The transitional state equation was used to calculate the variations in entropy and enthalpy 54 .
By plotting log (C.R/T) versus 1000/T, Fig. 5 shows the SCPs compounds in their transitional state.Slopes determine enthalpy, and the intersection of the lines [log(R/Nh) + ∆S * a /2.303R] determines the activation entropy of the process.The findings analysis was compiled in Table 3. Data in Table 3 showed that the E * a increased as the SCP's chemical dose was increased and was found to be higher than that of the control solution.The physical adsorption of the SCPs compounds on the CS surface is what causes this increase.The results in Table 3 showed Log k/T ,mg cm 2 min -1 1000/T,K -1

SCP1 SCP2
Figure 5. illustrates the plots of (log k corr /T) versus 1/T for the dissolution of CS with and without modified dosages of SCPs.
Vol:.( 1234567890) www.nature.com/scientificreports/ that SCPs compounds result in negative entropy values, and these negative values showed that the activated complex in the rate-determining state preferred association over dissociation 55 .The results confirm the existing thermodynamic relationship between E * a and ∆H * a , which characterizes a unimolecular process" 56 .
The computed value (2.4 at 25 °C) and expected value (in Table 3) are very similar.The inhibitors thereafter had a similar effect on E * a and ΔH * a .

Open circuit potential (OCP) measurements
The OCP versus time curves for C-steel corrosion in 1.0 M HCl are shown in "Fig.6 in both the absence and presence of various concentrations of derivatives of supramolecular coordination polymers (SCP1 and SCP2).
The potential for an unconstrained solution is seen to decline over time and stabilize at a value of − 435 mV/ SCE for SCP1 and − 430 mV/ SCE for SCP2, respectively, at about 200 s.This behavior can be explained by the corrosive compounds that emerge on the surface of the CS as a result of its degradation.In other words, when supramolecular coordination polymers (SCP1 & SCP2) are present at concentrations between 1 and 21 × 10 −6 M, the potential of SCP2 decreases, then increases, and then swiftly stabilizes over time, whereas the potential of SCP1 increases at first before reaching steady state after around 200 s.The disintegration of the oxide coating and the development of a protective film on the metallic surface can both be used to explain these phenomena.
(11)  www.nature.com/scientificreports/ In inhibited solutions, the potentials obtained moved to values more positive than those found in uninhibited solutions, according to a careful inspection of the OCP curves".This suggests that these substances have cathodic inhibitory effects.

PDP tests
In 1.0 M HCl medium at 25 °C, the PDP test is conducted with and without varying concentrations of synthetic substances (SCP1 & SCP2)."Table 4 displays the PDP parameters data, and Fig. 7 shows drowning.Figure 7 shows the polarization curves with and without SCP1 and SCP2 present.The cathodic and anodic overpotentials were decreased, and the major parallel displacement was moved to more negative and positive values with the addition of SCP1 and SCP2, respectively.The activation-controlled nature of hydrogen change is demonstrated by the parallel cathodic and anodic Tafel curves, and the presence of SCP1 & SCP2 has no effect on the reduction and dissolution processes 57 .Corrosion parameters were derived from the cathodic and anodic potential versus current density characteristics of the Tafel potential area 58,59 .The data in Table 4 showed that the current density decreases with increasing doses of the SCP1 and SCP2 compounds, indicating that a layer has formed on the CS surface.Additionally, the cathode and anode Tafel slopes do not indicate a significant change despite the presence of different dosages of SCP1 and SCP2 chemicals (Fig. 7).This can be explained by the fact that corrosion is caused by blocking the CS's surface's active spots.If there is a difference in corrosion potential (E corr ) values between the presence and absence of synthetic molecules of more than 85 mV, the inhibitor molecules are classified as cathodic or anodic, but this did not happen since the displacement in corrosion potential values is less than 85 mV.However, a little change in the E corr (63 mV) and a small change in (ß a & ß c ) on the rise in the dose of the used inhibitors revealed that these compounds work as mixed type inhibitors 60,61 .The corrosion current density dropped when the doses of synthetic compounds were raised.The (η p %) was calculated from PDP curves using Eq. 3. Molecular size, shape, and contact mode are just a few of the factors that influence inhibitory efficiency 62 .
The relationship of molecule size, structure, and functional group explains the high level of inhibitory activity observed.SCP1 came first in the ranking of (η p %), followed by SCP2 (SCP1 > SCP2).

EIS tests
At 25 °C in an acid medium, EIS studies with and without SCP1 & SCP2 inhibitors were carried out.Figure 8 displays the impedance values of the CS as discovered via comparable circuit studies using various SCP1 and SCP2 chemical dosages.Constant phase elements (CPE) are used in this circuit to produce several homogenizations that are not the best for preventing electrode corrosion, such as grain boundaries, surface impurities, and roughness (a decrease in polishing).Using the equation below, the capacitance double layer (C dl ) was produced": where f max is the maximum frequency.Table 5 displays the results from the impedance data for CS in 0.1 M hydrochloric acid in both the presence and absence of various dosages of the SCP1 and SCP2 compounds.The graphs that Nyquist and Bode discovered for CS when SCP1 and SCP2 were not present and when they were present at various doses are displayed in Figs. 9, 10, respectively.According to the Nyquist plots in Fig. 9, the circle's radius increases when the dose of SCP1 and SCP2 compounds rises.Consequently, an increase in the thickness of the electrical double layer (C dl ) causes the increase in the charge transfer resistance (R ct ) in corrosion processes.As a result of the single time constant in impedance spectroscopy, this illustrates a single capacitive loop in the applied frequency range.Charge transfer resistance was correlated with a higher frequency range, but film resistance produced by an inhibitor layer was correlated with a lower frequency range 63,64 .In our case, during the adsorption process while the inhibitor was present, a very thin layer formed on the metallic surface.
Because of frequency dispersion and microscopic roughness of the electrode surface, Nyquist curves for CS in an uninhibited solution flatten in the presence of inhibitors.The semi-circular Nyquist plot of an unconstrained solution indicates that the charge transfer resistance appears to have been the controlling component in the CS corrosion process.However, to illustrate the polarization resistance (R p ) between the metal and outer Helmholtz plane in the presence of inhibitors, the depressed semi-circular Nyquist plot is taken into consideration.According to the current finding, a high resistance has been established as a result of the SCP1 and SCP2 compounds adhering to the CS-solution/interface 65 .The heterogeneity of the CS surface and the frequency dispersion are responsible for the Nyquist curves' departure from semicircles 66 .Table 5 shows that the data for C dl decreases as the dose of SCP1 and SCP2 compounds increases.This decrease in C dl can be attributed to a local dielectric constant decrease or an increase in the thickness of the electrical double layer 67 ."The n value assesses the roughness or inhomogeneity of the solid surface.The n value increases in the 1 M HCl electrolyte relative to the reference electrolyte when SCP1 and SCP2 are combined (0.978-0.990), which can be interpreted as a little reduction in ( 12) Figure 8.The impedance data is fitted using the equivalent circuit.www.nature.com/scientificreports/surface heterogeneity 68,69 .This is caused by SCP1 and SCP2 compound molecules adhering to the solution's CS/interface.From Eq. 4, the EIS parameters and (% η R ) were computed.The low Chi-squared values (Table 5) obtained for all of the results show that there is good agreement between the fitted results and the experimental data.Chi-squared was used to measure how accurately the fitting result was achieved.Figure 9 makes it obvious how well the experimental and theoretical curves are fitted".These results are generally in agreement with the potentiodynamic polarization results.

EFM tests
EFM stands out for its unusual speed and accuracy in calculating current data 70 .Figure 11 displays the EFM of CS in 1.0 M HCl solution together with different dosages of the synthetic inhibitor SCP1.Similar curves were also obtained for a second SCP2 (not shown).The higher current peaks can be used to measure EFM parameters like (CF-2 and CF-3), (c and a), and (i corr ).The fact that the CF is more similar to the accepted data supports the accuracy of the calculated data 71,72 .The percentage, which was computed and given in Table 6, rises when the synthetic compound is improved.The results in Table 6 show that when concentration rises, there is a discernible fall in current density, which increases percent.This method was used to obtain the following information: There is a discernible decrease in the corrosion current's strength and an obvious rise in the% η with an increased dose of synthetic chemicals.The percentage obtained by applying ML, PDP, and EIS techniques is in the best agreement with that found by EFM tests.The percentage attained with ML, PDP, and EIS techniques is the closest to that found by EFM tests.www.nature.com/scientificreports/

Surface analysis
Scan electron microscopy (SEM) analysis Using SEM, the morphology of the steel surface was examined to ascertain whether the inhibition was brought on by the development of an organic coating.The surface with a protective film was examined using SEM on the CS specimens after 24 h at 25 °C in 1.0 mol/L HCl solution alone and with adding the optimal concentration (21 × 10 −6 mol/L) of SCPs (Fig. 12).After being submerged in the corrosive liquid, the surface of the CS metal surface became increasingly corroded with numerous deep cracks (Fig. 12a).This is because the metal in the test solution has dissolved.On the other hand, after the addition of (SCPs) to the test media, the surface became smoother with tiny, deep fractures (Fig. 12b, c).These data suggest that the inhibition is brought on by the development of a persistent, adherent deposit that stops the electrolytes from reaching the steel surface 73 .

Atomic force microscope (AFM) analysis
One may assess the surface roughness of coupons on an angstrom scale thanks to the atomic or near-atomic resolution surface topography afforded by the AFM technique."This approach is effective for examining the surface analysis of both inhibited and uninhibited carbon steel surfaces.A 3-D AFM image of the exterior of CS subjected to 1.0 M HCl for 24 h with and without the optimal SCPs level measured is shown in Fig. 1.After being submerged in 1.0 M HCl without an inhibitor for 24 h, the common roughness of the surface of C steel was measured and determined to be 467.57nm.In Fig. 13, a 3D image of the CS surface is shown while being exposed to the highest doses (21 × 10 −6 M) of SCP1 and SCP2, bringing the roughness to 91.3 and 102.7 nm, respectively".This decrease in roughness suggests that the surface of CS has grown a protective film 74 .

Quantum chemical parameters
The lower energy band gap value, "which is represented in the energy band gap ΔE g (ΔE = E HOMO E LUMO ), indicates that organic molecules are highly reactive and exhibit excellent corrosion behaviour on the surface of CS.An analysis of the impact of SCPs molecule's orientation on inhibition performance was conducted using density function theory (DFT).As shown in Fig. 14, the optimized geometry, HOMO surface, and LUMO surface of studied inhibitors can be found.The parameters HOMO (E H ), LUMO (E L ), and dipole moment (μ) for MOFs gradients were directly obtained from DFT (Table 7).Equations 13-18 were used to calculate the energy gap (ΔE), electronegativity (χ), global hardness (η), global softness (σ), the fraction of electron transfer (ΔN) and back-donation (ΔE back-donation)", was calculated as Koopmans's theorem 1 from the next balance: Numerous articles 75,76 have discussed how higher values of "E HOMO and lower values of E LUMO determine the greater electron-donating and accepting abilities of an inhibitor.Inhibitors are more reactive when a lesser value of ΔE is present.In this instance, SCP1' ΔE value is lower while higher values for SCP2.In comparison to SCPs molecules, these values suggest that SCP1 molecule has a high degree of reactivity.Metals and inhibitors can be understood using the number/fraction of electron transfer (ΔN).If the ΔN value of an inhibitor is higher, it is found to have a stronger capability of donating electrons to metallic surfaces.Compared to SCPs molecules, SCP1 exhibits greater amounts of ΔN in the gaseous phase, indicating that SCP1 exhibits a stronger inhibitory effect.

Monte Carlo (MC) simulation
MC modeling is a good method for calculation the most stable adsorption conformations of a SCPs. Figure 15 illustrates the simulation findings for the investigated SCP, which are described in Table 8. Figure 15 depicts the adsorbed molecule's most favorable confirmation on the CS metal surface (1 1 0)."Furthermore, the molecules stated are adsorbed on the metal surface from the motive, which is rich in inhibitory molecule electrons.The interactions between the occupied orbitals of the examined SCPs and the vacant orbitals of CS (110), which are reflected by energy adsorption values (E ads ), of the rigid energy (E rigid ), of the deformation energy (E def ), and energy ratio values (dE ads /dN i ) of the inhibitors, which is equivalent to the energy of substrate-adsorbate configurations where one of the adsorbate components has been removed are collected in Table 8.Adsorption energy values that are more negative indicate a highly stable and strong connection between adsorbed molecules and metal.When two materials are mixed during the adsorption process, an electron, ion, or molecule (adsorbent) is attached to the solid surface, adsorption energy is defined as declining energy 77,78 .As shown in Table 8, the greater adsorption energy of SCP1 rather than SCP2 on the hardened Fe surface predicts heavy adsorption of SCP molecules, forming a stable adsorbed layer that protects the iron from decomposition.The tabulated adsorption energies are -3868.456and -3598.362kcal/mole for SCP1, SCP2 respectively.The outputs show that the two inhibitors are efficient adsorptive inhibitors taking in respect that the better one is SCP1 which is attuned with the experimental results".Based on theoretical modeling it's obvious that SCPs based proved to be powerful inhibitors for the CS which is confirmed by experimental and spectral investigation.www.nature.com/scientificreports/

Anti-corrosion mechanism
The initial stage of the inhibitory action in acid media is adsorption on the metal surface 59 .The majority of studies on inhibition postulate that the unoccupied d-orbitals of the metal and the inhibitor's π-electrons will form a donor-acceptor surface complex 79 .SCP2 has two aromatic rings and four N atoms, whereas inhibitor SCP1 contains two aromatic rings and six N atoms.Inhibitors can either be cations (i.e., protonated species) or neutral substances in aqueous acidic solutions.There are two main categories of adsorption that might be considered.The removal of water molecules from the metal surface, the sharing of electrons between N-atoms and Fe, as well as between π-electrons from aromatic rings and the open d-orbitals of Fe, are all steps in the chemisorption process that might lead to the neutral form of the inhibitor attaching to the metal surface.On the other hand, it is well known that the CS surface is positively charged in acidic environments 80 .Protonated inhibitors have a strong time adhering to the positively charged CS surface due to electrostatic repulsion.Since  www.nature.com/scientificreports/chloride ions are more readily adsorbed, they provide the solution an excess negative charge and favor more protonated inhibitor adsorption due to the lower number of hydrations they possess.In other words, the inhibitors' ability to inhibit may be improved by the synergistic interaction between Cl − and the inhibitors.When the protonated inhibitors are deposited on the metal surface, the following things could occur: The development of a coordinate bond due to the partial transfer of electron from N-atoms to the metal surface and the protonated inhibitors may combine with newly formed Fe 2+ ions on the CS surface to produce a metal-inhibitor complex [Inh-Fe] (2+z)+81 .These complexes might bind to the surface of the CS utilizing Van der Waals forces, where they will create a corrosion-preventing shielding film".The film covers both the anodic and cathodic reactive sites on the CS surface, inhibiting both reactions simultaneously.SCP1 > SCP2 in percentage inhibition, this is due to i) the higher molecular weight of SCP1 than SCP2 ii) the presence of 6 donating N atoms in SCP1 than 4N atoms in SCP2 and iii) the presence of double Cu and Sn atoms in SCP1 than in SCP2 and as known the effectiveness of the sacrifice is increased by including additional electropositive metals in the organic framework.On the other hand, the organic structure creates a shield over the metal surface that prevents corrosion (Supplementary file 1).

Conclusions
The following conclusions may be drawn from the values we gained from theory and experimentation: 1.The synthesis and characterization of the supramolecular coordination polymers (SCPs) were conducted.2. By increasing the concentration of SCPs the η% increases and vice versa with raising temperature.
3. These substances exhibit mixed sort inhibitory behavior, as seen by the PDP curves.4.These chemicals adhere to the Henry model and are physically adsorbed on the CS surface. 5.The development of a protective coating from the SCPs on the CS surface was confirmed by SEM and AFM measurements.6.There is agreement between theoretical investigations, electrochemical measurements, and ML.

Figure 1 .Figure 2 .
Figure 1.ML-time diagrams for the dissolution of the CS in 1.0 M HCl solution in the absence an attendance of altered doses of SCPs at 25 °C.

Figure 3 .
Figure 3. Log K ads versus 1/T for the liquefaction of CS in 1.0 M HCl in the existence of SCP1 &SCP2.

Figure 4 .
Figure 4. shows plots of the dissolution of CS with and without different dosages of SCPs (log k corr vs. 1/T).

Figure 6 .
Figure 6.Variation of E OCP versus time for CS in the 1.0 M HCl solutions in the absence and presence of various concentrations of the SCP1 & SCP2 at 25 °C.

Figure 9 .Figure 10 .Figure 11 .
Figure 9.The Nyquist bends for CS dissolution 1.0 M HCl with and absence of altered doses of SCP1 &SCP2 at 25 °C.

Figure 15 .
Figure 15.Adsorption shapes of the SCPs molecules on CS surface using Material Studio software (version 7.0).

Table 1 .
Outcome data of ML of the CS in 1.0 M HCl solution for various doses of synthetic inhibitors (SCPs) after 120 min and at altered temperatures.

ads Table 2 .
lists the Henry parameters for the adsorption of synthetic composites on CS surface at various temperature conditions.

Table 3 .
lists the parameters of thermodynamics obtained from the Arrhenius and transition state equations.

Table 4 .
Parameters determined from the PDP for the corrosion of CS at 25 °C in both the absence of adding altered dosages of SCP1 and SCP2.

10 6 M i corr , μA cm −2 − E corr , mV vs SCE β a mV dec −1 − β c mV dec −
E, mV (vs SCE)Figure7.Shows the PDP bends for CS dissolution at 25°C in the absence and adding of altered dosages of SCP1 and SCP2.

Table 5 .
lists the EIS parameters for dissolving CS in 1.0 M hydrochloric acid both with and absence of several dosages of SCP1 and SCP2.

Table 6 .
EFM data for CS dissolution 1.0 M HCl with and absence of changed doses of SCP1 &SCP2.

Table 7 .
Quantum chemical data for SCPs under study.

Table 8 .
MC parameters of adsorption of SCPs molecules on CS (110) surface.